Fixing unit for photocopy machines with improved guiding means



Feb. 28, 1967 B. D. EISNER 3,306,595 FIXING UNIT FOR PHOTOCOPY MACHINESWITH IMPROVED GUIDING MEANS Filed Feb. 26, 1964 5 Sheets-Sheet lINVENTOR. BURTON D. EISNER BY 57 W0%, MM,W LZ AQM Feb. 28, 1967 B. D.EISNER 3,306,595

FIXING UNIT FOR PHOTOCOPY MACHINES WITH IMPROVED GUIDING MEANS Flled Feb26 1964 5 Sheets-Sheet 2 INVENTOR. BURTON D. EISNER BY 214%, MM, wwwmFeb. 28, 1967 B. D. EISNER 3,305,595

FIXING UNIT FOR PHOTOCOPY MACHINES WITH IMPROVED NS GUIDING MEA 5Sheets-Sheet 5 INVENTOR.

A'rrvs.

Filed Feb. 26, 1964 United States Patent 3,306,595 FIXING UNHT FORPHQTOCQPY MAtIHlNES WlTH IMPRQVED GUlDlNG MEANS Burton l). Eisner,Highland Park, IlL, assignor to American Photocopy Equipment Company,Evanston, Ill., a

corporation of Illinois Filed Feb. 26, 1964, Ser. No. 347,464 3 Claims.(Cl. 263-6) The present invention relates machines and, moreparticularly, guiding means for the fixing unit of anelectrophotographic copying machine.

The electrophotographic printing process employed in office photocopymachines and the like generally comprises the steps of uniformlycharging the surface of a photoconductive coating on a suitablephotocopy sheet, focusing a light image on the charged surface so as todischarge the portions irradiated by the light rays while leaving theremaining portions in a charged condition, thereby producing a latentelectrostatic image, developing the latent image by applying a developerpowder which adheres selectively to the charged areas, and then fixingthe developed image on the photocopy sheet, such as by heating thedeveloper powder. The developer powder conventionally includes a minorproportion of a heat settable resin which, upon being heated, causes thepowder to firmly adhere to the surface of the sheet. A suitable machinefor carrying out such a copying process is described in detail incopending application Serial No. 209,122, filed July 11, 1962, now US.Patent No. 3,159,- 735, entitled, Fixing Unit for Photocopy Machines,and assigned to the assignee of the present invention.

While use of the apparatus referred to above is found to produce copiesof a quality heretofore unattainable, it has been found that under somecircumstances the photocopy paper has a tendency to buckle under theinfluence of the applied heat in the fixer unit. This problem may beencountered when the copy sheets have high and variable moisturecontent. For example, the copy sheets may pass through the machinesmoothly during normal weather conditions, and then begin to buckle andhang up in the machine when the moisture content in the atmosphereincreases above a certain level. This buckling of the sheets, whichoccurs in the fixing unit, not only jams the machine, With all theattendant production losses and maintenance costs, but also produces apotential fire hazard.

When attempts are made to restrict the curling or buckling of the copysheet by the use of physical guides, one of the main problemsencountered is that the guides which engage the face or image-bearingside of the copy sheet tend to mar or blemish the heat-softened coating.For example, in certain cases the guiding members may have a scrapingeffect which simply removes the softened coating from the areas engagedby the guides. Moreover, with certain types of rotating guides, it hasbeen found that the guides develop tires of soft material which producevarious types of longitudinal marks on the copy sheet. In some cases thesoft material deposits on the copy sheet, producing black lines whichdeface the developed image; in other cases, the soft material in thetire picks up additional developer powder, producing blank lines runningthrough the developed image.

It is, therefore, a main object of the present invention to provide animproved'fixing unit which effectively prevents buckling of the copysheets under the influence of the applied heat. Accordingly, it is alsoan object to provide such a fixing unit which elfectively preventsmachine jamming and avoids all the attendant production losses andmaintenance costs. A related object is ,to

generally to photocopy to an improved paper provide such a fixing unitwhich passes the copy sheets smoothly and rapidly therethroughregardless of the moisture content in the copy sheets.

It is another object of the invention to provide a fixing unit havingimproved paper guiding means which prevent the heated copy sheets frombuckling and becoming hung up in the machine. It is a further object toprovide such guiding means which do not have any deleterious effect onthe copy sheets. A more particular object is to provide such guidingmeans which do not produce any substantial undesirable marks or lines onthe softened coating containing the developed image, and which does notremove or pick up any of the softened coating material. Another objectis to provide such guiding means which do not distort or mar thedeveloped image on the softened surface coating.

Still another object of the invention is to provide a fixing unit havingimproved paper guiding means which provides high interfacial tension andlow thermal conductivity and substantially eliminates sliding frictionbetween the copy sheet and the engaging surface of the guiding means. Arelated object is to achieve an extremely small area of engagementbetween the copy sheet and the guiding means. Another object is toprovide such a guiding means which has a relatively low thermalcapacity.

A further object of the invention is to provide an improved paper guidefor fixing units which substantially improves both the overallreliability and production capabilities of the machine and the qualityof the copies produced. In this connection, it is another object toprovide such a guiding means which has a relatively simple constructionand extremely long life, whereby replacement and maintenance costs areminimized.

Other objects and advantages of the invention will become apparent uponreading the attached detailed description and appended claims and uponreference to the drawings, in which:

FIGURE 1 is a simplified vertical section of an electrophotographiccopying machine employing the present FIG. 2 is an enlarged verticalsection taken through the fixing and finishing unit of the machine inFIG. 1 and showing the associated developing unit;

FIG. 3 is a side elevation view taken along line 3-3 in FIG. 2 andshowing the paper guiding means which engage the image side of thevertical copy sheets;

FIGS. 4 and 5 are side and end elevation views, respectively, of thepaper guiding assembly removed from the machine of FIGS. 1 through 3;

FIG. 6 is an enlarged perspective view of the guiding means which engagethe back side of the copy sheet in the machine of FIG. 1; and

FIGS. 7, 8 and 9 are perspective, side, and end views, respectively, ofthe guiding emans which engage the front of the copy sheet in themachine of FIG. 1.

While the invention has been described in connection with a preferredembodiment, it will be understood there is no intention to limit theinvention to the embodiment shown but, on the contrary, it is intendedto cover the various modifications and alternatives included within thespirit and scope of the appended claims.

Turning now to FIG. 1 of the drawings, an electrophotographic copyingmachine intended for ofi'ice use includes a frame 11, a base 12, and ahousing 13. At the front of the housing, two inlet slots are provided, afirst slot 14 for the original and a second slot 15 for the copysheet,with the two sheets, indicated at 16, 17, being fed in together,faceto-face. These sheets are separated in the machine, and the copysheet passes through a charging unit 18 where the face of the sheetacquires an overall static electric charge.

The original 16 is fed into the illuminating station 19 at the same timethat the copy sheet 17 is brought into the exposing station 20. Lightfrom a source not shown illuminates the original, with the image thereonbeing refiected by a mirror and lens assembly (not shown) onto themoving copy sheet and with the speed of the original correspondingexactly to the speed of the copy sheet. Subsequently, the original isdischarged into a return chute 22, while the copy sheet is conveyedupwardly by transfer rollers 23, 24 forcing its way through .a flexibleclosure flap 25 which is in the bottom of the trough 26 of thedeveloping unit 27. Such trough contains a charge of toner mix in theform of toner particles temporarily adherent to larger magneticparticles which act as a carrier. The mix clings to the surface of thedeveloping cylinder 29 in the form of soft tufts or bristles by reasonof the magnetism induced by an external permanent magnet.

Because of triboelectric phenomena, the toner particles are attracted tothe charged areas on the sheet leaving behind the magnetic carrierparticles, which latter particles, however, serve to prevent depositionof toner power in the uncharged areas on the sheet. Consequently, thecopy sheet, with the developed image thereon, passes upwardly into thefixing and finishing unit 40.

The particular heating arrangement shown in the fixing unit 40 (see FIG.2) utilizes back fixing, with the radiant heat source located at theback of the sheet, but it will be apparent that the invention is notlimited thereto and includes the possibility of front fixing or acombination of the two. In the present instance, the heat source is inthe form of an electrically heated radiation producing lamp 41 whichextends lengthwise within a reflector 42. The surface of the reflector42 is elliptical with the lamp 41 being positioned at one of the foci sothat the heat tends to be concentrated on the paper over a narrowhorizontal band. It will be apparent that the temperature and powerdissipation of the lamp 41 may be optimized depending on the speed oftransporting the copy sheet on a particular machine. While atransporting speed on the order of one inch per second may be used,studies show that the present fixing unit finishing arrangement iscapable of operating at a speed of much higher than this and up toapproximately three or even four inches per second. If desired, areflector may be used opposite the heat source to reflect incidentradiant heat back toward the face of the sheet. Extensions 45, 46 on thereflector are provided to maintain the fixing space at relatively hightemperature throughout to provide what may be termed oven effec Meansare, however, provided for preventing excess heat build up, particularlywhen the unit is operated over long periods of time. In the presentinstance, this is accomplished by forming the reflector 42 in arelatively massive reflector member 47 which is formed of aluminum orother good conducting material, and by providing an adjacent, closecoupled heat sink 48 in the form of an internally finned chamber throughwhich air is forced longitudinally under slight pressure. Acorresponding heat sink 49 is provided on the opposite side of thefixing unit and is also supplied with a source of cooling air.

In order to press the fused particles of pigmented toner into thesoftened resinous coating on the copy sheet, a pair of smothly surfaceddriven rollers 50 and 51 of good conducting material are mounted forrotation in the frame plates 52 immediately adjacent the heat applyingmeans. These rollers 50, 51 have a nip 53 which lies in the path of themovement of the advancing sheet. More specifically, the rollers arearranged sufliciently close to the source of heat so that the toner inthe surface of the paper are in the softened or yieldable state at thetime of the engagement by the rollers, and the rollers are biasedtogether with a force which is suflicient to press the toner intointimate engagement with the surface material.

In the practice of this invention, there is provided an improved guidingsystem including a first guiding means engaging the back of the copysheet and a second guiding means engaging the face or image-bearing sideof the copy sheet, the second guiding means being located sufficientlyclose to the first guiding means to restrict the buckling of the heatedsheet whereby jamming of the machine is effectively prevented, thesecond guiding means comprising a plurality of rotatable guiding membershaving low thermal conductivity and mounted to rotate in the directionof movement of the copy sheet, the rotatable guiding members also havinga very fine sheet-engaging edge, whereby high interfacial tension andlow thermal conduction is provided between the face of the copy sheetand the rotatable guiding members. Thus, there is provided a firstguiding means comprising an array of guide wires 54 engaging the back ofthe copy sheet adjacent the heat source, and a second guiding meanscomprising a plurality of spaced rotatable glass beads 55 shaped toprovide a fine peripheral edge 55a which engages the heat-softened faceof the copy sheet.

Turning attention first to the first guiding means, which engages theback of the copy sheet, there is provided in front of the reflectormember 47 a plurality of spaced generally vertical guide wires 54secured to top and bottom headers 56 and 57, respectively, such as bywelding. To maintain the wires 54 in position, the bottom header 57 isfitted into notches 58 in the frame plates, while the upper header 56 issecured by a spring clip 59. As will be apparent, this enables theentire assembly of guide wires 54 to be quickly removed for access tothe fixing region, such as for replacement of the lamp. While it hasbeen stated above that the wires 54 are generally vertical, it ispreferred to arrange the wires in herringbone pattern as illustrated inFIG. 6, with the wires diverting somewhat outwardly and upwardly withrespect to the center line. It has been found that this arrangement ofthe wires tends to keep the copy sheet flat, particularly where one ofthe corners of the advancing edge of the copy sheet has been turned overor is dog-eared and might, therefore, become caught on one of the wiresor headers. The action of the diverging guide wires is to tend tostraighten out the corner, keeping it flat in the plane of the sheetready for engagement with the nipping rollers. Equally important,keeping in mind that the wires 54 are in the path of radiation, the heattransferred from the wires to the copy sheet tends to be distributedover the surface of the sheet rather than being concentrated alongnarrow longitudinal paths.

In accordance with one of the aspects-of the present invention, bucklingor curling of the copy sheet 17 is effectively prevented by positioningthe second guiding means, which engages the face or image-bearing sideof the sheet, sufiiciently close to the first guiding means to maintainthe copy sheet in a fixed vertical plane and thereby restrict anytendency of the sheet to buckle or curl as it is heated. The secondguiding means comprises a plurality of guide members 55 rotatablymounted on brackets 60. In order to prevent the curling or buckling ofany substantial portion of the copy sheet 17 as it passes through thefixing region, both the wires 54 and the guide members 50 must belocated at spaced points across substantially the entire width of thesheet 17. The transverse space between the wires 54 and the peripheriesof the guide members 55 must be sufliciently narrow to prevent theundesired curling or buckling, and this space may vary somewhat withdiflerent applications.

Referring to FIGS. 3 to 9, the rotatable guide members 55 in theparticular construciton illustrated are secured to axles 61 by means ofclinch pins 62. The axles 61 are rotatably mounted in the supportingbrackets 60 which, in turn, are riveted to a mounting plate 63, as byrivets 64. This entire assembly is then secured within the fixing regionby bolting the mounting plate 63 to the wall of the heat drain, as bybolts 65. Since the axles 61 are loosely mounted in the brackets 60, theslightest grazing contact between the advancing copy sheet 17 and therotatable guiding members 55 suflicies to rotate the members 55. Thus,there is practically no sliding friction between the image side of thecopy sheet 17 and the rotatable guide members 55.

In the particular guiding system illustrated, the rotatable members 55are arranged in two staggered horizontal series (see FIGS. 3 and 4). Thelower series of members 55 is located at the lower portion of the fixingregion and includes only one rotatable member 55' on each of fourbrackets 60, the brackets being spaced across the full width of the copysheet 17. The upper series of rotatable members 55" is located at aboutthe middle of the fixing zone and, since the temperature of the copysheet is highest at that point, it includes two rotatable members 55" oneach of the four brackets 100. Of course, it will be understood thatadditional horizontal series of rotatable guide members may be provided,or additional members may be provided in each horizontal series,depending on the size of the fixing region, the particular temperatureemployed, the type of paper employed, and the like.

In accordance with one aspect of this invention, there is provided aguiding member for engaging the softened coating on the image side ofthe copy sheet without producing any substantial deleterious marks orlines thereon, and without removing nor picking up any of the softenedcoating material thereon. Thus, there is provided a plurality of smallspaced rotatable glass beads 55 made of a hard low-heat-conductingmaterial such as glass, ceramic, or the like and mounted to rotate inthe direction of movement of the copy sheet 17. The contacting surfaceof the glass beads 55, i.e., the surface which engages the softenedcoating on the image side of the copy sheet, should be extremely narrowor fine and is preferably discontinuous. In other words, the area ofengagement between the copy sheet and the guiding glass beads should beas small as possible and also discontinuous. In the particularconstruction illustrated in the drawings, the small contact area isprovided by employing beads which are beveled to a generally doubleconical shape so as to form a narrow contact ridge 55a (see FIGS. 6-8)around the middle of each bead in the common plane of the cone bases.The discontinuity is provided by employing beads which are faceted onthe conical surfaces so that the contact ridge 55a has a serrated orserpentine edge which engages the copy sheet intermittently rather thancontinuously.

It has been found that when the insulating glass beads are used as guidemembers according to this invention, they completely eliminate bucklingor curling of the copy sheet without any substantial marring of thedeveloped image. Even in the case of copy sheets exhibiting extremelyhigh buckling tendencies, the copies emerge from the machine with onlysporadic minute dot marks appearing on the copy. Machine jamming iscompletely avoided, with resultant substantial increases in machineproductivity and corresponding decreases in down time and maintenancecost.

Studies have been made in order to ascertain the reasons for theunexpected superior performance of the glass guiding members describedabove, and it is believed that the unusual effectiveness of this guidingsystem is due at least in part to the extremely low interfacial tensionand low thermal conductivity between the copy sheet and the glass beads,and the low thermal capacity of the glass beads. Thus, the fine contactridge of the glass guiding members, although in a region of hightemperature, does not tend to maintain the high temperature on engagingthe face of the sheet, but rather tends to immediately assume thetemperature of the sheet. This is in contrast to the effect of aconductive guide member, such as a metal disc, which would have theeffect of supplying heat of fusion to the image being fixed, portionsengaging the back of the copy sheet and second 6 of the fused materialbeing lifted off as the disc rotates for a progressive build up of atire.

It will be apparent from the foregoing description that the nature ofthe guiding members which engage the image side of the copy sheets ismuch more critical than that of the guiding members which engage theback side of the copy sheets. Thus, if desired and without departingfrom the invention, the guide wires 59 may be dispensed with and thepaper may be held forwardly by an air blast directed against the backside of the sheet from a series of horizontally arranged holes directlyopposite the heat source; however, this requires a correspondingincrease in capacity of the blower which is used for cooling purposes.Alternatively, a vacuum may be drawn in the C- shaped reflector by avacuum line.

What is claimed is:

1. In a fixing unit for a photocopy machine of the type in which acoated copy sheet having the electrostatic image thereon is developed byapplication of a fusible pigmented powder to the charged areas, thecombination comprising a heating unit for increasing the temperature ofsaid fusible pigmented powder sufiiciently high to fuse said powder andfix the developed image, transporting mechanism for advancing the copysheet past said heating unit, and a guiding system for directing thecopy sheet through the fixing unit, said guiding system including firstguiding means engaging the back of the copy sheet and second guidingmeans comprising a plurality of faceted double conical glass beadshaving serrated ridges formed by the bases of the cones, said serratedridges engaging the softened powder on the copy side of the copy sheet,said first and second guiding means being located sufiiciently close toeach other to restrict the buckling of the heated sheet whereby jammingof the machine is effectively prevented.

2. In a fixing unit for a photocopy machine of the type in which acoated copy sheet having a latent electrostatic image thereon isdeveloped by application of a fusible pigmented powder to the chargedareas, the combination comprising a heating unit for increasing thetemperature of said fusible pigmented powder sufficiently high to fusesaid powder and fix the developed image, transporting mechanism foradvancing the copy sheet through a fixing region adjacent to saidheating unit, and a guiding system within said fixing region fordirecting the copy sheet therethrough, said guiding system includingfirst guiding means engaging the back of the copy sheet and secondguiding means engaging the coated image-bearing side of the copy sheet,said first and second guiding means being located sufficiently close toeach other to maintain said copy sheet in a fixed plane and to restrictthe buckling of the heated sheet whereby jamming of the machine iseffectively prevented, said second guiding means comprising a pluralityof rotatable glass beads spaced both transversely and longitudinallyalong the path of said sheet through said fixing region, said beadsbeing of generally double conical shape with the common plane of thebases of said double cones forming a narrow guiding edge around theperiphery of said beads for engagement with said sheet, and the conicalsurfaces of said beads being faceted so as to provide discontinuousengagement between said guiding edge and said copy sheet.

3. In a fixing unit for a photocopy machine of the type in which acoated copy sheet having a latent electrostatic image thereon isdeveloped by the application by a fusible pigmented powder to thecharged areas, the combination comprising a heating unit for increasingthe temperature of the said fusible pigmented powder sufiiciently highto fuse said powder and fix the developed image, transporting mechanismfor advancing the copy sheet through a fixing region adjacent to saidheating unit, and a guiding system for directing the copy sheet throughsaid fixing region, said guiding system including first guiding meansguiding means engaging the coated image-bearing side of the copy sheet,said first and second guiding means being located sufliciently close toeach other to maintain said sheet in a fixed plane and to restrict thebuckling of the heated sheet whereby jamming of the machine iseffectively prevented, said vfirst guiding means comprising a pluralityof laterally spaced guide wires oriented in the direction of movement ofsaid sheet and interposed between the face of the sheet and said heatingunit for defining a certain minimum spacing between the heat source andthe back of the sheet, said second guiding means comprising a pluralityof thermally insulating rotatable glass beads spaced both longitudinallyand transversely along the path of said sheet said beads being ofgenerally double conical shape with the common plane of the bases ofsaid double cones forming a narrow guiding edge around the periphery ofsaid beads for engagement with said sheet, and the conical surfaces ofsaid beads being faceted so as to provide discontinuous engagementbetween said guiding edge and said copy sheet.

References Cited by the Examiner UNITED STATES PATENTS 3,055,229 9/1962Mecham 198-230 X 3,159,735 12/1964 Eisner et al. 219347 3,190,643 6/1965Taillie 27175 X 3,219,799 11/1965 Trumbull et a1. 219-216 X 3,239,2203/1966 Lot et al 198167 X FREDERICK L. MATTESON, JR., Primary Examiner.

JOHN J. CAMBY, Examiner.

1. IN A FIXING UNIT FOR A PHOTOCOPY MACHINE OF THE TYPE IN WHICH ACOATED COPY SHEET HAVING THE ELECTROSTATIC IMAGE THEREON IS DEVELOPED BYAPPLICATION OF A FUSIBLE PIGMENTED POWDER TO THE CHARGED AREAS, THECOMBINATION COMPRISING A HEATING UNIT FOR INCREASING THE TEMPERATURE OFSAID FUSIBLE PIGMENTED POWDER SUFFICIENTLY HIGH TO FUSE SAID POWDER ANDFIX THE DEVELOPED IMAGE, TRANSPORTING MECHANISM FOR ADVANCING THE COPYSHEET PAST SAID HEATING UNIT, AND A GUIDING SYSTEM FOR DIRECTING THECOPY SHEET THROUGH THE FIXING UNIT, SAID GUIDING SYSTEM INCLUDING FIRSTGUIDING MEANS ENGAGING THE BACK OF THE COPY SHEET AND SECOND GUIDINGMEANS COMPRISING A PLURALITY OF FACETED DOUBLE CONICAL GLASS BEADSHAVING SERRATED RIDGES FORMED BY THE BASES OF THE CONES, SAID SERRATEDRIDGES ENGAGING THE SOFTENED POWDER ON THE COPY SIDE OF THE COPY